The present invention relates to balloons for medical devices and medical devices utilizing such balloons. More particularly, the present invention relates to medical or surgical balloons and catheters using such balloons, particularly those designed for angioplasty, valvuloplasty and urological uses and the like. The balloons of the present invention can be tailored to have expansion properties which are desired for a particular use and can be inflated to a predetermined diameter and still be resistant to the formation of pin holes and leakage.
In the past, polyethylene, polyethylene terapthalate and polyamide balloons have been used with medical catheters. Polyethylene balloons are particularly advantageous because they can be heat bonded to a like-material substrate and have a relatively low tip diameter, that is the profile of the tip at the connecting joint between the balloon and the catheter can be fairly small. Also, the polyethylene balloons are soft so that they can pass through blood vessels without trauma. Moreover, polyethylene balloons are resistant to the propagation of pin holes, primarily because the walls are thick. But since they are thick, they are large and pass by tight lesions only with great difficulty.
Balloons of polyethylene terapthalate provide low deflated profiles and can have thin walls because such materials have high tensile strengths and adequate burst strength. On the other hand, polyethylene terapthalate balloons require adhesives to bond them to the catheters and adhesive bonding frequently is not dependable and it thickens the catheter at the point of the bond. Moreover, polyethylene terapthalate can have poor pin hole resistance largely due to the very thin walls.
According to the present invention, it has been discovered that the drawbacks of the polyethylene and the polyethylene terapthalate balloons of the prior art can be remedied through the use of laminated balloon constructions which comprise a tubular body formed of a plurality of co-extruded and coextensive layers of different polymeric materials.
According to one aspect of the invention, the multi-layered balloon combines the advantages of both materials in a balloon, but does not have the disadvantages of either. The balloon includes a layer of a relatively thick, biaxially oriented ethylenic polymeric material such as polyesters, polycarbonates, polyethylene terapthalate and their copolymers, or polyamides such as Nylon. These materials constitute a base structural layer (or layers) and give the balloon its tensile strength and provide for xe2x80x9cwearxe2x80x9d resistance. The base structural layer may have a thickness between about 0.2 and 1.0 mil. or higher. A second layer is co-extruded with the base structural layer and is coextensive therewith. The second layer preferably is a polyolefin such as polyethylene and copolymers thereof and can be heat-bonded to a catheter, that is adhesives need not be used. The heat bondable second layer can be disposed on one and preferably both sides of the base structural layer.
In accordance with another aspect of the present invention, the base structural layer again is a material that does not itself readily thermally bond to a polyethylene catheter tubing. In those cases, sleeves of mutually bondable materials are slipped over the joints between the catheter and the balloon and the sleeves are heated to join the balloon to the sleeve and simultaneously join the sleeve to the catheter whereby to act as a fluid-tight seal between the catheter and the balloon.
With regard to multilayered balloons, the second layer (or layers) which is disposed on the base structural layer and co-extruded therewith can also serve as a barrier between the base structural layer and the environment. For example, when a polyamide such as Nylon is used as the base structural layer, a thin layer of maleic anhydride-modified ethylenic polymers such as Plexar can also be co-extruded with it. When layers are disposed on both sides of the base structural layer they keep moisture from effecting the Nylon""s properties. Additional layers sometimes may also be co-extruded to bind and tie dissimilar layers together in the co-extrusion operation. When Nylon is used, for example, no tying layers are necessary between it and the heat bondable layer. In other cases, however, as when polyester or polycarbonate polymers are used as the base structural layer, adhesion enhancement may be necessary. Such adhesive enhancement may take the form of ultraviolet light irradiation of the product or the incorporation of a co-extruded tying adhesive layer.
With regard to the use of a multi-layered sleeve to join the balloon to the catheter, any conventional medical balloon material can be used that does not bond to the catheter without adhesives. The multi-layered sleeve can be formed of a base layer of the same material as the balloon with a polyethylene layer disposed on at least the inner side of the sleeve. The polyethylene will adhere to both the catheter and the balloon and form a joint with heat treatment alone.
According to the present invention, the balloons have advantages of both the polyethylene and the materials of the base structural layer. When polyethylene terapthalate is the base, very thin walls can be used with high burst strength. For example, when a typical 3.0 mm. diameter maleic anhydride-modified ethylenic polymer is coated on a Nylon base structural layer, the resulting balloon can have a wall thickness of 0.5 mil. and a low deflated profile which is comparable with polyethylene terapthalate balloons and is much lower than polyethylene balloons. When using Nylon, the material that is used is biaxially orientable and has higher tensile strength than polyethylene material, thereby resulting in a much thinner wall for comparative burst strength.
It has been found that pin hole resistance of the construction of the present invention is comparable to polyethylene and substantially superior to polyethylene terapthalate. A balloon co-extruded with Selar has superior abrasion resistance and pin hole resistance then polyethylene terapthalate balloons. Polyamide material is superior to polyethylene terapthalate and polyethylene materials in pin hole resistance. The balloon itself is soft for non-traumatic passage through blood vessels and is comparable to polyethylene because polyamide is not as stiff as polyethylene terapthalate.
In a specific embodiment of a multilayered extruded balloon, it has been found that the use of the above mentioned Selar PT resin, a trademarked compound (preferably available as Selar PT 4368 from E. I. Dupont de Nemaurs Co. of Wilmington, Del.) as a layer disposed on the base structural layer (or blended with polyethylene terapthalate) will make the balloon more resistant to abrasion and provide it with a softer feel. Selar co-extrusion in multi-layered balloons diminishes pin hole formation and will minimize failure when working with calcified lesions. Moreover, the Selar may be used as the inner layer of the balloon for use with procedures which include internal electrodes or radiopaque markers which could puncture it.